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{-# LANGUAGE TypeFamilies #-}
module T2693 where
type family TFn a :: *
-- Boiled down version
f :: Maybe ()
f = do
let Just x = undefined :: Maybe (TFn a)
let n = fst x + fst x
return ()
f2 :: Maybe ()
f2 = do
let x :: TFn a
x = undefined
let n = fst x + snd x
return ()
-- Close to the original report
data PVR a = PVR {pvrX :: Int} deriving (Eq)
g :: () -> Maybe (TFn a)
g _ = undefined
h :: Maybe ()
h = do pvs <- mapM g undefined
let n = (map pvrX pvs) `min` (map pvrX pvs)
undefined
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